Re: [PATCH v9 00/22] Enable FRED with KVM VMX

[David Woodhouse]

On Thu, 2026-05-07 at 15:53 +0200, Maciej Wieczor-Retman wrote:
> 
> My theory is that after 'int3' call the FRED event is handled elsewhere and %rdi
> is not preserved. So the original version of the assembly looks okay but I was
> thinking that int3 has side effects.
> 
> Below is the test output of the RIPs not matching when running the original,
> does that help in any way?

Ah right, of course!

+"fred_entrypoint_kernel:\n"
+	"movq %rsp, %rdi\n"
+	"call fred_handler\n"
+	".byte 0xf2, 0x0f, 0x01, 0xca\n"	/* ERETS */
+	".popsection\n"

That needs to save the %rdi it's scribbling on, plus all the callee-
clobbered registers that fred_handler() might use.

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